1. Field of the Invention:
The present invention relates generally to a process for manufacturing a semiconductor device and is directed more particularly to a process for manufacturing a semiconductor device in which a semiconductor substrate implanted with ions is annealed in a short period of time to form an electrically activated region thereon.
2. Description of the Prior Art:
A prior art technique, in which the crystal defects in an ion implanted region is restored to electrically activate the implanted atoms or ions, is typically an annealing method using an electrical furnace. This prior art method is such that a number of semiconductor substrates implanted with ions are set on a quartz board or the like and then are subjected to the heating process within an electrical furnace at, for example, 800.degree. to 1200.degree. C. for more than 10 minutes to provide an electrically activated region in each of the substrates.
This method is productive in view of the fact that a number of substrates can be processed at the same time, but is defective in view of the fact that since the substrates to be annealed have large thermal capacity, nonuniformity is generated in electrically activated layers which are provided in a short period of heating.
Further, even in the case where the controllability of the profile of an ion implanted region is attempted to be utilized in making a semiconductor element, redistribution phenomenon is generated in the ion implantation profile by the prior art long time heating. As a result, the advantage of the ion implantation is damaged.
Further, upon manufacturing a semiconductor device thermally unstable such as GaAs compound semiconductor atoms such as Ga, As forming the substrate are vaporized during long time heating at high temperature to form a thermal conversion layer on the surface of the substrate which damages the electrical activation of the ion implanted region.
Recently, as a new annealing processing method for an ion implantation region, a laser anneal method, for example, has been studied which can electrically activate an ion implanted region in a very short period of time (such as in a nano second to a micro second). The mechanism thereof is considered that a semiconductor substrate absorbs the energy of laser light and converts the same to heat energy to achieve the annealing process for the substrate. In this case, however, the light absorption coefficient of the semiconductor substrate much depends on the wave length of the laser light and also on the crystal property of the semiconductor substrate (varied in response to the amount of implanted ions), which requires that the laser output must be changed in accordance with semiconductor substrates to be annealed.
Further, when a laser light is radiated on a multilayer structure such as SiO.sub.2 --Si structure, polycrystalline Si--Si structure and so on to anneal the same, there is the reflection of the laser light on, for example, the surface of Si and an interference effect determined by the wave length of the laser light, the thickness of a SiO.sub.2 layer on Si and so on. Hence, the laser output during annealling must be different.
According to the present anneal by laser light, a laser beam is focussed with several 10 .mu.m scans a semiconductor substrate in two dimension to anneal it uniformly. However, no uniform anneal is achieved due to the fluctuation, flicker or the like of the laser light. If a semiconductor substrate can be radiated by a laser with a large spot, this case, however, requires a very intensive laser output.